The present invention relates in general to combustible fuel slurries containing liquid hydrocarbon fuel and comminuted coal in the liquid hydrocarbon. More particularly, it relates to the prevention or substantial reduction of the settling of the comminuted coal particles in the liquid hydrocarbon.
The United States possesses the largest proven mineral coal deposits in the world. The reserves are enormous and have a combined BTU value far exceeding that of the liquid reserves in the Middle East nations. Yet the United States continues to import a substantial portion of its energy requirements from abroad, and has not yet fully utilized its coal resources.
Efforts to increase coal utilization have included combining comminuted coal to fuel oil to form a slurry which may be fed to a furnace, boiler, or other oil burning device. The coal must be of a relatively small particle size; coal fines may be used in the mixtures to solve a long-standing disposal problem. Large particles will have a tendency to settle more rapidly and will further cause abrasion as they pass through the fuel feed nozzles and may even clog the nozzles.
The most pertinent prior art references include U.S. Pat. No. 4,201,552, issued to Rowell et al on May 6, 1980, hereinafter referred to as Rowell. Rowell discloses that quaternary ammonium compounds having a morpholinium or other cyclic structure are useful as stabilizers for coal-oil slurries, but does not disclose any non-cyclic quaternary stabilizers. Japanese application No. 32886/78, by Nakamura et al, was published on Oct. 1, 1979, and is also directed to cyclic ethoxylated quaternary ammonium salts said to be useful as coal oil mixture stabilizers. Examples of suitable stabilizers disclosed thereon include imidazoline and diimidazoline compounds, the latter typically having substituted benzenesulfonate as the anion.